Method for Predicting and Preventing Shrinkage Cavity of Iron Casting

ABSTRACT

A method for predicting and preventing occurrence of shrinkage cavity in an iron casting of any of various shapes or in each part of an iron casting precisely prior to casting. The shape of an iron casting is approximated entirely or partially to a rectangular parallelepiped or a cube, to the sum of the two long sides is divided by the short side to determine a shape coefficient, and occurrence of shrinkage cavity is predicted by determining whether the value exceeds a predetermined value (determination coefficient) or not.

TECHNICAL FIELD

The present invention relates to a method for predicting and preventingshrinkage cavity of an iron casting.

BACKGROUND ART

Various types of methods for predicting shrinkage cavity have been posedfor many years. Typical examples thereof include an evaluating methodproposed by Tivolinov of Russia and an evaluating method proposed byNiiyama. The former uses modulus which is a value obtained by dividingthe volume of a casting by the surface area thereof. The latter uses avalue obtained by dividing a temperature gradient G by the square root Rof a cooling rate.

However, these methods for predicting shrinkage cavity can be effectivefor cast steel, nonferrous metal or the like having no expansion causedby the generation of graphite. However, the methods are not necessarilyeffective for cast iron caused by the generation of graphite.

Therefore, Yoshida et al. has proposed Patent Document 1 as a method fordetermining occurrence of shrinkage cavity of spheroidal graphite castiron. This method measures eutectic crystal solidification times of theinside and surface of the casting, and determines whether the shrinkagecavity exists or not from the overlapping degree of the eutectic crystalsolidification times, i.e., the Massey degree. Patent Document 2proposes a method for obtaining a solid phase rate from the number ofgrains and graphite diameter of graphite and using the solid phase ratefor determining the shrinkage cavity.

The determining methods proposed by Yoshida et al. are useful to someextent for determining the tendency of the shrinkage cavity of thespheroidal graphite cast iron. However, it is difficult to predict theshrinkage cavity using such methods. This is because the shrinkagecavity occurs in a larger iron casting in these methods, which disagreeswith the fact discovered by the present inventors that no correlationexists between the shrinkage cavity and the size of the product when themold strength is sufficiently high.

A “hot spot method” using a solidification simulation has been usuallyemployed as the method for predicting shrinkage cavity. This methodfocuses on easy occurrence of shrinkage cavity in a non-solidified metalpart since molten iron cannot be resupplied to the non-solidified metalpart when an island of molten iron broken from the other, i.e., loops(referred to as “hot spot” in an island of the non-solidified metalsurrounded by a metal having solidified circumference) having a closedtemperature constant-temperature line or solidification line are formedin the casting in a solidification process. Since the cast steel andnonferrous metal having no expansion caused by the crystallization ofgraphite has an extremely high probability that the shrinkage cavityoccurs in the “hot spot” part, the “hot spot method” has been widelyused as a high-precision determining method. However, when the “hotspot” is formed in the cast iron having expansion caused by thecrystallization of graphite, this part does not necessarily become theshrinkage cavity.

Patent Document 1: Japanese Patent Application Laid-Open No. 10-296385

Patent Document 2: Japanese Patent Application Laid-Open No. 05-96343

DISCLOSURE OF INVENTION Problem to be Solved by the Invention

As the methods for preventing shrinkage cavity, a feeder head and achiller etc. are used. As for the feeder head ordinary used is a methodfor calculating a modulus of a product and erecting a feeder head havinga larger modulus than the modulus of the product. Therefore, there is aproblem that the size of the feeder head is almost the same as that ofthe product, and the yield becomes extremely worse. Cast iron hardlycauses occurrence of shrinkage cavity as compared with cast steel. Forthis reason, when the amount of the feeder head is lessened, theshrinkage cavity occurs, and after all, the shrinkage cavity occurs inmany cases if the same feeder head as that of the cast steel is noterected. For the method for preventing shrinkage cavity using thechiller, the place of the shrinkage cavity can be moved by constructingthe chiller, but the shrinkage cavity cannot be lost. This is becausethe cast iron has the complicated occurrence mechanism of the shrinkagecavity and the mechanism is not sufficiently resolved.

Various types of methods for predicting shrinkage cavity have beenproposed as described in the prior art. However, the method forpredicting shrinkage cavity, which is appropriate to the property ofcast iron and has high accuracy, has not been established at present.Also, a method for preventing shrinkage cavity, which is efficientlyappropriate to the property of cast iron, has not been proposed even ifthe method can predict the shrinkage cavity.

It is an object of the present invention to provide means for preciselypredicting existence or nonexistence of occurrence of shrinkage cavityin a casting of any of various shapes or in each part of the casting,and capable of performing a suitable casting method and changing aproduct shape for the casting predicted to cause the occurrence of theshrinkage cavity or each part of the casting so that a sound casting canbe obtained.

Means for Solving the Problem

The present inventors investigated the existence or nonexistence ofoccurrence of shrinkage cavity and carried out various types ofexperiments such as solidification simulation and measurement oftemperature for various casting products having different sizes,materials or shapes to resolve that the shrinkage cavity occurs in thecasting product having what type of shape. The means will be illustratedusing an example of a block of a rectangular parallelepiped. The presentinventors have discovered that the occurrence of the shrinkage cavity isprevented regardless of the size of the casting when a value (herein,referred to as “shape coefficient”) obtained by dividing the sum of twolong sides of the rectangular parallelepiped by the length of aremaining short side is not more than a certain numerical value. Thepresent inventors have discovered that the certain numerical valueherein is about 8 in ordinary spheroidal graphite cast iron whichcontains no elements promoting the shrinkage cavity such as Cr and Mo,and also that the value changes as Cr or Mo increases.

The present inventors have also discovered that when the casting producthas a shape which is not the rectangular parallelepiped block, the shapemay be approximately considered to be the rectangular parallelepiped.For example, in the case of the spherical product, the shape may beconsidered as a cube with one side to which a sphere is inscribed beingequal to the diameter of the sphere, and in the case of a product havinga cylindrical shape, the shape may be considered as a rectangularparallelepiped of which two long sides are equal to the diameter of acircle. The shape may be considered as a rectangular parallelepipedobtained by developing the cylinder in the case of a doughnut-shapedcylinder having a hole therein. The present inventors have discoveredthat a product of a combination of various shapes may be considered bydividing the parts of the product.

As described above, the existence or nonexistence of the shrinkagecavity can be determined from only the shape of the product. Also, thepresent inventors have discovered that the occurrence of the shrinkagecavity can be predicted in each of closed elliptical loops as follows.Solidification analysis or the like is performed to obtain a shapecoefficient of each of the closed elliptical loops in a solidificationdistribution chart obtained from a temperature distribution or asolidification time distribution in the solidification of the castingproduct, followed by determining whether the value is not more than 8.

The use of such a method can determine whether or not shrinkage cavityoccurs in “hot spot” which is an island of molten iron broken from theother, i.e., loops having a closed temperature constant-temperature lineor solidification line in the casting in the solidification process.Naturally, the shape coefficient may be determined as an ellipticalsphere. However, the shape coefficient may be determined byapproximating an elliptical sphere having a closed Rugby ball shape tothe rectangular parallelepiped.

A method for determining the shape coefficient of each of the closedelliptical loops in the solidification simulation using a computer is asfollows.

As one method, there is a method for measuring the size of an arbitraryelliptical loop on a screen by operation of a mouse or the like using asolidification distribution chart obtained from a temperaturedistribution or solidification time distribution due to solidificationsimulation to obtain a shape coefficient.

As the other method, there is used a method for specifying an arbitraryelliptical pool to determine a shape coefficient. For example, the wholesolidification time is divided to a plurality of times, and theelliptical loop in arbitrary time of them is specified. This ellipticalloop is composed by elements in the mesh cutting. It is determined howmany elements exist in X, Y and Z directions of this mesh to determine ashape coefficient of the elliptical loop.

Examples of the other methods include a method for processing data ofextracted arbitrary elliptical loop in another place to evaluate theshape and to calculate a shape coefficient.

Thus, many means can be considered as the method for determining a shapecoefficient of an elliptical loop using a computer.

Of course, the industrial greatest worth of the present invention isthat the shrinkage cavity can be predicted. The other worth thereof isthat a method for preventing the shrinkage cavity is proposed. That is,the present inventors have discovered that occurrence of the shrinkagecavity is prevented by dividing a product so that a shape coefficient isset to not more than 8 using a chiller or a feeder head, or both thechiller and the feeder head.

The example of the rectangular parallelepiped will be illustrated. Whena plate of 800×400×80 mm is used as an example, it is turned out that ashape coefficient of the plate is (800+400)/80=15 and the shrinkagecavity occurs when the shape coefficient is 8 or more. When the plate isdivided into four by the chiller, the shape coefficient is(400+200)/80=7.5, and the shrinkage cavity does not occur when the shapecoefficient is 8 or less. The phenomenon as the description could beobserved even in the actual product test. As for the chiller availableis a method for constructing a chiller directly brought into contactwith molten iron. However, since one loop of blocked solidification needonly to be divided into four, a method for constructing the chillerwhich is not directly brought into contact with the molten iron has alsono problem. When the construction area of the chiller is excessivelyincreased, and the closed solidification loop is not divided into four,the shrinkage cavity naturally occurs. It is, therefore, necessary topay attention to the shrinkage cavity. When the feeder head is used, thefeeder heads are constructed at four places of the above plate, and theclosed solidification loop may be divided into four.

The shape coefficient of whether the shrinkage cavity occurs or not isnaturally changed when containing elements such as Cr and Mo forpromoting the shrinkage cavity, or conversely, according to the amountof C preventing the shrinkage cavity. Also, the shape coefficient ischanged depending on, for example, the strength (correctly, the strengthof a mold at a high temperature) of the mold, and the rigidity of a moldframe. The value of the shape coefficient for determining the shrinkagecavity is preferably determined by considering these conditions.However, in the case of an organic self-hardening mold generally used,the experiment of the present inventors shows that the shape coefficientof about 8 needs only to be used. Even in flake graphite cast iron, theexistence or nonexistence of the shrinkage cavity can be determined bythe shape coefficient to construct a measure so as to prevent theshrinkage cavity from occurring.

To summarize the description, a first aspect of the present inventionprovides a method for predicting shrinkage cavity in an iron casting,the method comprising: determining a shape coefficient which is a valueobtained by dividing a sum of two long sides by a remaining short sidefrom a shape of a casting product; and confirming whether or not theshape coefficient is 8 or more to predict occurrence of the shrinkagecavity.

A second aspect of the present invention provides a method forpredicting shrinkage cavity in an iron casting, the method comprising:determining a shape coefficient of each of closed elliptical loops in asolidification distribution chart obtained from a temperaturedistribution or a solidification time distribution in a solidificationof a casting product; and confirming whether or not the shapecoefficient is 8 or more to predict occurrence of the shrinkage cavityin each of the closed elliptical loops.

A third aspect of the present invention provides the method forpredicting shrinkage cavity according to the second aspect, wherein thesize of the elliptical loop is measured on a screen using thesolidification distribution chart obtained from the temperaturedistribution or the solidification time distribution due to asolidification simulation, thereby to calculate the shape coefficient.

A fourth aspect of the present invention provides the method forpredicting shrinkage cavity according to the second aspect, wherein theshape coefficient is calculated from the number in X, Y and Z directionsof elements constituting the elliptical loops divided by mesh cutting byuse of the solidification distribution chart obtained from thetemperature distribution or the solidification time distribution due toa solidification simulation.

A fifth aspect of the present invention provides a method for predictingshrinkage cavity in an iron casting, the method comprising: dividing aproduct using a chiller or a feeder head or using the chiller and thefeeder head together when a shape coefficient is more than 8 to set theshape coefficient to 8 or less.

A sixth aspect of the present invention provides the method forpredicting and preventing shrinkage cavity according to any of the firstto fifth aspects, wherein the shape coefficient of whether the shrinkagecavity occurs or not is determined by components of the casting, aproperty of a mold and a cast position.

Effect of the Invention

The present invention founds a new concept of a shape coefficient, andcan use the shape coefficient to simply predict occurrence of theshrinkage cavity with extremely high accuracy. Even when the castingcomponents, the type of the mold, the cast position and the like aredifferent, the occurrence of the shrinkage cavity can be predicted bythe shape coefficient. Furthermore, when the occurrence of the shrinkagecavity is predicted, the occurrence of the shrinkage cavity can belogically prevented by using effectively the chiller or the feeder head.Therefore, the present invention has effects such as the reduction ofdefective fraction in the iron casting, the improvement in yield and theshortening of delivery time, and can produce spheroidal graphite castiron efficiently at low cost.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A, 1B, 1C, 1D, 1E, 1F and 1G describe the shape approximation ofa casting product.

FIG. 2 is a graph showing the relationship between a shape coefficientof a rectangular parallelepiped and shrinkage cavity.

FIG. 3 is a graph showing the relationship between a shape coefficientof a disc-shaped object and shrinkage cavity.

FIG. 4 is a graph showing the relationship between a shape coefficientof a cylindrical body and shrinkage cavity.

FIG. 5 is a graph showing the relationship between shape coefficients ofrectangular parallelepipeds in different cast positions and shrinkagecavity.

FIG. 6 is a graph showing the relationship between shape coefficients ofrectangular parallelepipeds of different molten iron components andshrinkage cavity.

FIG. 7 is a graph showing the relationship between shape coefficients ofrectangular parallelepipeds and shrinkage cavity in a case of usingdifferent molds.

FIG. 8 shows an example predicting shrinkage cavity in a computersimulation.

FIG. 9 shows an example of a section in which elliptical loops exist.

FIG. 10 shows a dialog for measuring a width (w), a length (l) and athickness (t_(MS)).

FIG. 11 shows an example of a section in which elliptical loops exist.

FIG. 12 shows an example of elliptical loops of a solidificationdistribution chart.

FIG. 13 shows an example of a cube circumscribed to elliptical loops.

FIG. 14 shows a dialog for automatically calculating a shapecoefficient.

FIG. 15 shows a method for constructing a chiller to prevent shrinkagecavity.

FIG. 16 shows a method for constructing a feeder head to preventshrinkage cavity.

FIG. 17 shows an example using a mistake chiller.

FIG. 18 shows an example using a correct chiller.

FIG. 19 is a flow chart of a method for predicting and preventingshrinkage cavity in an iron casting product.

BEST MODE FOR CARRYING OUT THE INVENTION

The above and other objects, aspects and advantages of the presentinvention will make apparent, to those skilled in the art with referenceto the following detailed description in which the preferred specificexamples suitable to the principle of the present invention are shown asembodiments and the accompanying drawings. As a matter of course, thepresent invention, which is described in the following detaileddescription, is not limited to the embodiments shown in the accompanyingdrawings.

Hereinafter, the present invention will be described in detail based onspecific examples.

The present invention fundamentally uses a shape coefficient (F)determined as a value obtained by dividing the sum of two long sides bya remaining short side. As most understandable examples, in a case of ablock having a casting shape of a rectangular parallelepiped, a valueobtained by dividing the sum of a width (W) and length (L) of the blockby a thickness (T_(MS): the shortest side of three sides) is a shapecoefficient. The shape of a block having a shape other than therectangular parallelepiped may be approximately considered to be therectangular parallelepiped.

FIG. 1 shows examples in the case of determining a shape coefficient ofeach of castings having various shapes.

FIG. 1( a) shows a cube, and all of a width (W), length (L) and height(T_(MS)) become a length of one side of the cube. FIGS. 1( b) and 1(c)respectively show the case where a plate of a rectangular parallelepipedis horizontally placed and the case where the plate of the rectangularparallelepiped is vertically placed, with the width (W), the length (L)and the height (T_(MS)) being taken. FIG. 1( d) shows a disc having aheight of less than a diameter. As for the shape of the disc, thediameter of the disc is considered to be the width (W) and the length(L), and the height (wall thickness) is considered to be T_(MS) todetermine a shape coefficient. As shown in FIG. 1( e), in the case of acylinder having a height of not less than a diameter, the diameter ofthe cylinder is considered to be the width (W) and the height (T_(MS)),and the height of the cylinder is considered to be the length (L). Inthe case of a doughnut-shaped tube shown in FIG. 1( f), a tube isdeveloped to form a rectangular parallelepiped, and a shape coefficientis determined by respectively considering the height of the tube, thelength of the circumference and the thickness of the tube to be thewidth (W), the length (L) and T_(MS).

In FIG. 1( g) where the cylinder, the plate of the rectangularparallelepiped and the tube are combined, a cylindrical part, a platepart of a rectangular parallelepiped and a tubular part are respectivelyconsidered to be a cylinder, a plate and a tube. A shape coefficient ofeach of the parts may be determined by the above method, and it may bedetermined whether or not shrinkage cavity occurs in each of the parts.Also, a measure for preventing the shrinkage cavity to be describedlater may be performed for each of the parts.

FIGS. 2, 3 and 4 show experimental results obtained by measuring therelationship between a shape coefficient ((L+W)/T_(MS)) and an area rateof shrinkage cavity in test pieces having different shapes and sizes. Anordinary ductile iron casting (FCD600) is used for the material of thetest pieces, and a furan self-hardening mold is used for a mold. In theexperiment, the dimensions (width, length, thickness and diameter) ofthe test piece are changed as shown in Table of each of FIG. 2 to 4 toproduce some test pieces shown by numbers A, B and C, and to measure therelationship between the shape coefficient and the area rate of theshrinkage cavity for each of the test pieces.

FIG. 2 shows a plate test piece of a rectangular parallelepiped, FIG. 3shows a test piece of a disc shape, and FIG. 4 shows a test piece of atubular shape. FIGS. 2, 3 and 4 show that the shrinkage cavity occurswhen the shape coefficient ((L+W)/T_(MS)) is more than 8 and theshrinkage cavity does not occur when the shape coefficient is not morethan 8. That is, FIGS. 2, 3 and 4 show that the occurrence of theshrinkage cavity can be predicted by the shape coefficient in spite ofthe shape. Herein, when the shape coefficient causing no occurrence ofthe shrinkage cavity is referred to as determination coefficient, FIGS.2, 3 and 4 show that the determination coefficient is 8.

The present inventors also investigated whether or not there is thedifference in the shape coefficients causing no occurrence of theshrinkage cavity depending on a cast position, i.e., how to place acasting, i.e., the determination coefficients. FIG. 5 shows experimentalresults of the relationship between the shape coefficient ((L+W/T_(MS))and the area rate of the shrinkage cavity when the same casting (a plateof a rectangular parallelepiped as the test piece) is vertically andhorizontally placed. The test piece is an ordinary ductile iron casting(FCD600).

As shown in FIG. 5, when the shape coefficient is 8 or less, theshrinkage cavity does not occur in the test piece (number D1 of Table)horizontally placed. However, when the shape coefficient is 6 or less,the shrinkage cavity does not occur in the test piece (number D2 ofTable) vertically placed. Therefore, the determination coefficient is 8in the test piece horizontally placed, and the determination coefficientis 6 in the test piece vertically placed.

The reason why the difference in the determination coefficients appearsaccording to the cast position is believed to be based on the influenceof gravity. That is, it is turned that the shape coefficient(determination coefficient) causing no occurrence of the shrinkagecavity changes even in the casting having the same component and size.Therefore, a shape coefficient value for determining the shrinkagecavity is preferably determined by considering these conditions.

Next, the present inventors also investigated whether or not there isthe difference in the shape coefficients causing no occurrence of theshrinkage cavity when a ductile casting contains elements promoting theoccurrence of the shrinkage cavity. Mo is a well-known element promotingthe occurrence of the shrinkage cavity.

FIG. 6 shows experimental results of the relationship between the shapecoefficient and the area rate of the shrinkage cavity for three testpieces (numbers E1, E2 and E3 of Table) having different contents of Mo.

The experiment results show that the shrinkage cavity does not occur inthe ordinary ductile casting which does not contain Mo when the shapecoefficient is not more than 8. The experiment results also show thatthe shrinkage cavity does not occur at the shape coefficient of not morethan 6 when the ductile casting contains Mo of 0.3% by weight and at theshape coefficient of not more than 3 when the ductile casting containsMo of 0.6% by weight. That is, it is clear that the inclusion of theelements promoting the occurrence of the shrinkage cavity changes theshape coefficient (determining coefficient) causing no occurrence of theshrinkage cavity. The value of the shape coefficient for determining theshrinkage cavity is preferably determined by considering theseconditions.

The present inventors also investigated whether there is the differencein the shape coefficients causing no occurrence of the shrinkage cavity,i.e., the determination coefficients when the type of the mold isdifferent. FIG. 7 shows the relationship between the shape coefficientand the area rate of the shrinkage cavity when the type of the mold isdifferent (the numbers F1, F2, F3 and F4 of Table).

A plate of a rectangular parallelepiped is used as the test piece inFIG. 7, and the shrinkage cavity does not occur when the shapecoefficient is not more than 2 in a CO₂ type mold believed to have nohigh temperature strength. Next, the shrinkage cavity does not occurwhen the shape coefficient is not more than 6 in a greensand type moldhaving a low high temperature strength, when the shape coefficient isnot more than 8 in a furan type mold having a sand strength of 10kgf/cm² at a normal temperature, and when the shape coefficient is notmore than 10 in a furan type mold having a sand strength of 30 kgf/cm²at a normal temperature. That is, FIG. 7 shows that the shapecoefficient (determination coefficient) causing no occurrence of theshrinkage cavity is different according to the type of the mold. Thevalue of the shape coefficient for determining the shrinkage cavity ispreferably determined by considering these conditions.

FIG. 8 shows an example predicting shrinkage cavity using asolidification simulation due to a computer.

In the solidification simulation, a solidification distribution chart isobtained from a temperature distribution or a solidification timedistribution. A shape coefficient (f) can be calculated by respectivelymeasuring dimensions of a width (w), length (l) and thickness (t_(MS))from closed elliptical loops. As the elliptical loops, the innermostloop need not to be necessarily used, and the loops are preferably usedto a last solidification part from a last half solidification part (theelliptical loop used in the following description means the loops to thelast solidification part from the last half solidification part).

In the example shown in FIG. 8, the shape coefficient (F) determinedfrom the shape of the test piece is (200+200)/100=4, and the shapecoefficient (f) determined from the elliptical loop due to thesolidification simulation is also (60+60)/30=4. This result shows thatthe shape coefficient (f) determined from the elliptical loop of thesolidification distribution chart obtained from the solidificationsimulation is a value approximated to the shape coefficient (F)determined from the shape of the test piece. That is, the shrinkagecavity can be predicted based on the shape coefficient from thesolidification distribution chart by the solidification simulation dueto the computer. When the product shape is particularly complicated, theshrinkage cavity is effectively predicted based on such a solidificationsimulation. When the complicated shapes are combined, it is turned outthat a shape coefficient (f) of the elliptical loop occurring for eachof the shapes is determined and the shrinkage cavity may be predictedfrom the shape coefficient (f) thus determined.

(1) One Example of Methods for Measuring Width (w), Length (l) andThickness (t_(MS)) due to Solidification Simulation

There is shown an example of methods for measuring a width (w), length(l) and thickness (t_(MS)) required for calculating a shape coefficientdue to a solidification simulation in the present invention.

In the solidification simulation, the solidification distribution chartis obtained from the temperature distribution or the solidification timedistribution. First, as shown in FIG. 9, a section in which theelliptical loop exists is displayed for measuring the closed ellipticalloop from the obtained distribution chart. Next, the size of theelliptical loop is measured. The dialogs of U, V and W shown in FIG. 10in measuring the size are used. If “Measurement in U direction” of thisdialog is pushed on the screen, for example, the loop of an XY sectionviewed from an X direction is displayed. If “Measurement in V direction”is pushed, for example, the loop of a YZ section viewed from a Ydirection is displayed. If “Measurement in W direction” is pushed, forexample, the loop of a ZX section viewed from a Z direction isdisplayed. In the measurement of l, w and t_(MS) of the elliptical loop,a measurement starting position and a measurement end position arespecified on the screen using a mouse or the like. The measurement inthe thickness direction of the section displayed is performed bychanging the section to be displayed using the dialog of FIG. 10, asshown in FIG. 11. At this time, the measurement in three directions isrequired. However, since it is unknown which direction is the width (w),the length (l) and the thickness (t_(MS)), the system automaticallyconsiders that the shortest length is the thickness t_(MS) from themeasuring results of three directions. The system considers anddetermines that the others are the width (w) and the length (l). Whenthe measurement in three directions is completed, the shape coefficientis calculated by clicking a “calculation” button. A calculated value isdisplayed on a shape coefficient column of FIG. 10.

(2) One Example of Automatic Calculation of Shape Coefficient Due toSolidification Simulation

There is shown an example of methods for automatically calculating ashape coefficient due to simulation.

In the solidification simulation, a solidification distribution chart isobtained from a temperature distribution or a solidification timedistribution. The total frame number (a value for dividing how manytimes to the solidification end from the solidification start) and thedisplay frame number (a numerical value for displaying an island (loop)of what position of times divided to the solidification end from thesolidification start) are specified for obtaining (displaying) anarbitrary closed elliptical loop from the solidification distributionchart. Therefore, some islands shown in FIG. 12 are obtained. Theseislands mean an isothermal distribution or an equal solidification timedistribution. These islands are composed by elements divided by the meshcutting for the solidification simulation. As shown in FIG. 13, arectangular parallelepiped circumscribed to this island is calculated bycounting the number of elements in each of X, Y and Z directions. Awidth (w), a length (l) and a thickness (t_(MS)) are determined from therectangular parallelepiped, and the shape coefficient is automaticallycalculated.

Finally, the shape coefficient of each of islands can be determined byclicking a calculation button shown in FIG. 14. For example, it can bedetermined whether or not the shrinkage cavity occurs in a portion bycoloring blue to red for the shape coefficient and viewing whether theshape coefficient is high or low.

Of course, the present invention can predict the shrinkage cavity.However, the present invention also proposes a method for preventing theshrinkage cavity, and an example thereof is shown below.

FIG. 15 shows a construction example of a chiller preventing theoccurrence of the shrinkage cavity.

Since the test piece is an ordinary ductile iron (FCD600), and has acast position horizontally placed, the determination coefficient is 8.However, since the shape coefficient of the test piece is(400+800)/80=15, exceeding 8 in the example of FIG. 15, the shape causesthe occurrence of the shrinkage cavity. The chillers are constructedcrosswise at the upper and lower sides of the test piece, and thesolidification distribution chart was determined by the solidificationsimulation. An A-A′ section and a B-B′ section in FIG. 15 show that theclosed elliptical loop is divided into four. That is, four rectangularparallelepipeds divided by the chiller may be believed to solidifyindependently and respectively. Therefore, since the shape coefficientof the divided rectangular parallelepiped is (400+200)/80=7.5, that is,above 8, the occurrence of the shrinkage cavity can be prevented.

FIG. 16 shows one of construction examples of a feeder head forpreventing the occurrence of the shrinkage cavity.

Since the test piece having the same material and dimensions as those ofthe case of FIG. 15 is used, the shape coefficient of the test piece is15, and the shape causes the original occurrence of the shrinkagecavity. Four feeder heads having a diameter of 150 mm and a height of225 mm were constructed on the test piece, and the solidificationdistribution chart is determined by the solidification simulation. AnA-A′ section of FIG. 16 shows that the closed elliptical loop is dividedinto four. That is, even in this case, four rectangular parallelepipedsdivided by the feeder head may be believed to solidify independently andrespectively. A shape coefficient (F) of the divided rectangularparallelepiped is 7.5, and the occurrence of the shrinkage cavity can beprevented.

When the feeder head is generally constructed, it is considered that theclosed elliptical loop which is the last solidification part must beconfined in the feeder head. Therefore, the feeder head larger than theproduct is often erected. However, it is understood from the viewpointof the shape coefficient that even a small feeder head is sufficient aslong as the closed elliptical loop of the solidification distributionchart obtained by the solidification simulation is divided and the shapecoefficient of each of the parts divided by the feeder head or the shapecoefficient of the divided elliptical loop is a value which does notexceed the determination coefficient.

The chiller is generally used for preventing the shrinkage cavity.However, many wrong usages, i.e., many usages promoting the occurrenceof the shrinkage cavity exist. In the present invention, the right usageof the chiller, i.e., a method for logically preventing the occurrenceof the shrinkage cavity has been found by focusing attention on theshape coefficient.

FIG. 17 shows an example of a wrong usage of the chiller.

Since the shape coefficient (F) of the test piece is (240+400)/80=8, theshape does not essentially cause the shrinkage cavity. However, a methodis often adopted in the casting spot, which constructs feeder heads 10 aand 10 b at the upper and lower sides of the test piece and prevents theshrinkage cavity. In the method, the shrinkage cavity may increase bycontrast. When the solidification distribution chart is determined bythe solidification simulation in a state where the feeder heads 10 a and10 b abut on the upper and lower sides, the shape coefficient (f) of theclosed elliptical loop is (72+170)/13=19 as shown in an A-A′ section anda B-B′ section of FIG. 17, which shows that the shrinkage cavity occursin spite of constructing the feeder head.

On the other hand, FIG. 18 shows the right usage of the chiller.

The shape coefficient (F) of the test piece is (100+400)/50=10, and theshape causes the occurrence of the shrinkage cavity. The feeder heads 10a and 10 b are attached to both the sides of the test piece, andsimilarly, the solidification distribution chart is determined by thesolidification simulation. As shown in the A-A′ section and the B-B′section, the shape coefficient (f) of the closed elliptical loop is(17+60)/13=6, and the shrinkage cavity does not occur. Therefore, thesections show that the shrinkage cavity can be prevented by the ideabased on the shape coefficient in constructing the chiller.

FIG. 19 collectively shows a flow chart of the method for predicting andpreventing the shrinkage cavity in the present invention.

The method for predicting and preventing the shrinkage cavity of thepresent invention includes the following steps (1) to (6).

(1) The dimensions of two long sides (W, L) and remaining short side(T_(MS)) of the casting are measured. Alternatively, two long sides (w,l) of the closed elliptical loop and remaining short side (t_(MS)) arecalculated by the computer simulation.

(2) The shape coefficient [F=(W+L)/T_(MS)] is determined from W, L andT_(MS). Alternatively, the shape coefficient [f=(w+l)/t_(MS)] isdetermined from w, l and t_(MS).

(3) When the shape coefficient (F or f) is smaller than thedetermination coefficient (E, generally 8), the shrinkage cavity isdetermined as “nonexistence”.

(4) When the shape coefficient (F or f) is larger than the determinationcoefficient, the shrinkage cavity is determined as “existence”.

(5) When the shrinkage cavity is determined as “existence”, the productis divided by the chiller or the feeder head.

(6) The shape coefficient (F or f) is made smaller than thedetermination coefficient by repeating the processes (1) to (5).

The present invention founds a new concept of a shape coefficient, andcan use the shape coefficient to simply predict the occurrence of theshrinkage cavity with extremely high accuracy. Even when the castingcomponents, the type of the mold, the cast position and the like aredifferent, the occurrence of the shrinkage cavity can be predicted bythe shape coefficient. Furthermore, when the occurrence of the shrinkagecavity is predicted, the occurrence of the shrinkage cavity can belogically prevented by using effectively the chiller or the feeder head.Therefore, the present invention has effects such as the reduction ofdefective fraction in the iron casting, the improvement in extractionrate and the shortening of delivery time, and can produce the spheroidalgraphite cast iron efficiently at low cost.

INDUSTRIAL APPLICATION

Since the present invention can predict whether or not the shrinkagecavity is formed from the shape of the casting in the iron castingbefore the cast, and can previously prevent the shrinkage cavity, thepresent invention is useful in the iron casting technique.

1. A method for predicting shrinkage cavity in an iron casting, themethod comprising: determining a shape coefficient which is a valueobtained by dividing a sum of two long sides by a remaining short sidefrom a shape of a casting product; and confirming whether the shapecoefficient is not more than 8 or not to predict occurrence of theshrinkage cavity.
 2. A method for predicting shrinkage cavity in an ironcasting, the method comprising: determining a shape coefficient of eachof closed elliptical loops in a solidification distribution chartobtained from a temperature distribution or a solidification timedistribution in a solidification of a casting product; and confirmingwhether or not the shape coefficient is 8 or more to predict occurrenceof the shrinkage cavity in each of the closed elliptical loops.
 3. Themethod for predicting shrinkage cavity according to claim 2, wherein thesize of the elliptical loop is measured on a screen using thesolidification distribution chart obtained from the temperaturedistribution or the solidification time distribution due to asolidification simulation, thereby to calculate the shape coefficient.4. The method for predicting shrinkage cavity according to claim 2,wherein the shape coefficient is calculated from the number in X, Y andZ directions of elements constituting the elliptical loops divided bymesh cutting by use of the solidification distribution chart obtainedfrom the temperature distribution or the solidification timedistribution due to a solidification simulation.
 5. A method forpredicting shrinkage cavity in an iron casting, the method comprising:dividing a product using a chiller or a feeder head or using the chillerand the feeder head together when the shape coefficient is more than 8to set the shape coefficient to 8 or less.
 6. The method for predictingand preventing shrinkage cavity according to, claim 1 wherein the shapecoefficient of whether the shrinkage cavity occurs or not is determinedby a component of the casting, a property of a mold and a cast position.7. The method for predicting and preventing shrinkage cavity accordingto claim 2 wherein the shape coefficient of whether the shrinkage cavityoccurs or not is determined by a component of the casting, a property ofa mold and a cast position.
 8. The method for predicting and preventingshrinkage cavity according to claim 3 wherein the shape coefficient ofwhether the shrinkage cavity occurs or not is determined by a componentof the casting, a property of a mold and a cast position.
 9. The methodfor predicting and preventing shrinkage cavity according to claim 4wherein the shape coefficient of whether the shrinkage cavity occurs ornot is determined by a component of the casting, a property of a moldand a cast position.
 10. The method for predicting and preventingshrinkage cavity according to claim 5 wherein the shape coefficient ofwhether the shrinkage cavity occurs or not is determined by a componentof the casting, a property of a mold and a cast position.